Heretofore in wide use as motor vehicle air conditioner evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
Evaporators meeting such a demand are already known which comprise a heat exchange core composed of tube groups in the form of two rows arranged in parallel in the front-rear direction and each comprising a plurality of heat exchange tubes arranged at a spacing, an upper tank disposed at the upper end of the heat exchange core and having joined thereto the upper ends of the heat exchange tubes, and a lower tank disposed at the lower end of the heat exchange core and having joined thereto the lower ends of the heat exchange tubes, the lower tank having two headers arranged in the front-rear direction and having joined thereto the respective groups of heat exchange tubes, each group of heat exchange tube having lower ends joined to each header while being inserted through tube insertion holes formed in a top wall of each header, the top wall of the header being in the form of a segment of a cylindrical surface bulging upward at the midportion thereof with respect to the front-rear direction, the header having front and rear side walls each having a vertical planar upper portion, the two headers being interconnected by a connector, the upper portions of the front and rear walls of the adjacent two headers and the connector thereof providing a drain gutter extending in the left-right direction and having front and rear vertical side walls, the connector having drain holes extending therethrough (see the publication of JP-A No. 2003-214794).
However, the evaporator disclosed in the publication has the problem that the upper surface of the lower tank can not be drained of condensation water efficiently since the water fails to smoothly flow from the top surfaces of the headers of the lower tank into the drain gutter.
An object of the present invention is to overcome the above problem and to provide a heat exchanger wherein the upper surface of the lower tank can be drained of water with an improved efficiency when the exchanger is used as an evaporator.